1. Field of the Invention
The present invention relates to a liquid sealed vibration isolating device for use in an engine mount or the like for a motor vehicle, and more particularly, to the device capable of effectively decreasing noises produced by a cavitation phenomenon and of realizing high damping.
2. Description of the Related Art
In this kind of liquid sealed vibration isolating device, there is a possibility that negative pressure is developed in a primary liquid chamber when a heavy load is inputted. Then, the cavitation phenomenon that a portion of a hydraulic liquid is evaporated is created thereby producing noises together therewith. Therefore, various means capable of preventing the noises are proposed. As one of these means, an elastic movable diaphragm is arranged in a through hole provided in a partition member in such a manner that an outer peripheral portion of the diaphragm is able to be contacted with and separated from an inner wall of the through hole. When the high amplitude of vibration is inputted, the outer peripheral portion of the elastic movable diaphragm is deformed and projects into a secondary liquid chamber so as to form a gap for having a large amount of the hydraulic liquid leaked out therethrough (see a patent reference 1).    Patent reference 1: Japanese patent laid open publication No. 2006-132615.
By the way, in the construction using the elastic movable diaphragm, since the elastic movable diaphragm is elastically deformed even when the minute amplitude of vibration is inputted, a seal of the outer peripheral portion becomes imperfect and there is a possibility of causing a leak even at the time of pressurization, so that such leak gives rise to deterioration in damping performance. Therefore, the applicant has proposed the art that a relief valve is provided on the outer peripheral side with respect to a fixed portion having nothing to do with hydraulic pressure absorption of the elastic movable diaphragm. Incidentally, when this relief valve is formed by an elastically deformable film, there is a possibility that the relief valve, at the time of no leaking, is elastically deformed and absorbs the hydraulic pressure by hydraulic pressure fluctuation of the primary liquid chamber, depending on setting of its elastic force or the like.
However, for example, in the case where there is provided a damping orifice which liquid column resonates by the vibration of about 10 Hz so as to obtain high damping, it is thought there are cases that a function of the damping orifice is weakened by the hydraulic pressure absorption of the relief valve so that the predetermined high damping can not be accomplished. On the other hand, when the relief valve is hardened up to the level that is not elastically deformed, the function, as the relief valve, of preventing the cavitation phenomenon is hindered.
Therefore, the present invention aims to provide a liquid sealed vibration isolating device capable of obtaining the high damping while maintaining its original function of preventing the cavitation phenomenon through the relief valve.